最近由于升级服务器系统，我仓促中，保存了下mysql的数据文件就直接重装系统了，导致mysql也从8.0.20升级到了8.0.21，但是直接移动数据文件到mysql的数据目录没办法启动，只能暂时重装博客，导入mysql文件了，中间折腾了很久，找了n多方法，都不行最后，自己想着是不是重新装一个8.0.20的版本就ok，所以就开始了尝试之路
1. 下载对应的mysql包
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| wget https://downloads.mysql.com/archives/get/p/23/file/mysql-community-client-8.0.20-1.el7.x86_64.rpm
wget https://downloads.mysql.com/archives/get/p/23/file/mysql-community-libs-8.0.20-1.el7.x86_64.rpm
wget https://downloads.mysql.com/archives/get/p/23/file/mysql-community-common-8.0.20-1.el7.x86_64.rpm
wget https://downloads.mysql.com/archives/get/p/23/file/mysql-community-server-8.0.20-1.el7.x86_64.rpm
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2. 安装对应的包
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| rpm -ivh mysql-community-common-8.0.20-1.el7.x86_64.rpm
rpm -ivh mysql-community-libs-8.0.20-1.el7.x86_64.rpm
rpm -ivh mysql-community-client-8.0.20-1.el7.x86_64.rpm
rpm -ivh mysql-community-server-8.0.20-1.el7.x86_64.rpm
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3. 将备份的mysql 文件拷贝到新的mysql目录下
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| cp -r mysql /var/lib/mysql
#修改文件夹权限
chmod -R 755 mysql
#修改用户组
chown -R mysql:mysql mysql
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4. 尝试启动 mysqld
启动失败，查看mysql启动日志
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| tail -f /var/log/mysqld.log
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提示报错
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| If you are installing InnoDB, remember that you must create directories yourself, InnoDB does not create them.
2021-04-15T10:47:30.776403Z 1 [ERROR] [MY-012646] [InnoDB] File ./ibdata1: 'open' returned OS error 71. Cannot continue operation
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尝试删除ib_logfile* 删除ibdata*等文件
提示新的报错
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| Operating system error number 2 in a file operation.
[ERROR] [MY-012592] [InnoDB] Operating system error number 2 in a file operation.
2021-04-15T12:00:31.172856Z 1 [ERROR] [MY-012593] [InnoDB] The error means the system cannot find the path specified.
2021-04-15T12:00:31.172976Z 1 [ERROR] [MY-012594] [InnoDB] If you are installing InnoDB, remember that you must create directories yourself, InnoDB does not create them.
2021-04-15T12:00:31.173072Z 1 [ERROR] [MY-012646] [InnoDB] File ./ibdata1: 'open' returned OS error 71. Cannot continue operation
2021-04-15T12:00:31.173150Z 1 [ERROR] [MY-012981] [InnoDB] Cannot continue operation.
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和
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| 2021-04-15T12:02:26.565726Z 1 [ERROR] [MY-011971] [InnoDB] Tablespace 'innodb_undo_001' Page [page id: space=4294967279, page number=11] log sequence number 2122113581 is in the future! Current system log sequence number 17573900.
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修改配置文件 /etc/my.cnf 添加如下配置
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| innodb_force_recovery = 6
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binlog相关报错
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| mysqld: File './binlog.000062' not found (OS errno 2 - No such file or directory)
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删除 binlog文件但是没有清空 binlog.index文件里的内容，清空就好了
再次执行启动命令就成功了，然后执行数据导出操作
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| mysqldump -uroot -p --all-databases > all-databases.sql
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这样就能把之前的数据找回来了，对新的mysql数据库做数据导入就好了。
执拗前行